1. Field of the Invention
The present invention relates to a post-treatment liquid for inkjet recording, an image forming method, a cartridge and an image forming apparatus.
2. Description of the Related Art
An inkjet recording method has been rapidly spreading in recent years since it enables recording a color image on plain paper and at low running costs. However, this method has problems that image defects typified by letter bleeding (feathering) are likely to occur depending on combinations of an ink and a recording medium and also that image quality largely degrades such as degradation of beading quality on offset printing paper combined with a water-based ink since it has extremely poor absorbency of the water-based ink.
Also, when a color image is recorded by the inkjet recording method, color inks having different colors are superimposed one after another. This causes the color inks to smear or mix at a color boundary part (hereinafter referred to as color bleed), which is a problem of largely decreased image quality.
Thus, in order to increase image quality by solving these problems, image forming methods using a treatment liquid and an ink is proposed. For example, a method of discharging a treatment liquid from a head for uniform application of the treatment liquid, a method of pneumatically spraying, and a method of coating uniformly by controlling pressures of a coating roller and an opposing roller have been considered.
Further, regarding a treatment liquid used in a post-process after printing with an ink, a method including processes of a pre-treatment process, a printing process and a post-treatment process, wherein a UV varnish is sprayed particularly in the post-treatment process (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2004-330568), and a method of imparting image scratch resistance by coating an image-forming section with an overcoat liquid including a resin after printing have been considered (for example, see JP-A No. 2010-105187 and JP-A No. 2010-115854).
The method described in JP-A No. 2004-330568 above has problems of increased size of an apparatus, increased costs, and safety of materials. Also, the methods described in JP-A No. 2010-105187 and JP-A No. 2010-115854 have problems in ensuring discharge stability of the overcoat liquid including a resin from the head and increased costs of materials such as resin, and especially, scratch resistance of printed matters of offset printing paper using a water-based ink is not sufficient.
An oil-based ink is generally used on offset printing paper, but its use is restricted in view of resource conservation in recent years as well as safety. Also, in view of energy conservation, printing has been more favored with a water-based ink, and especially in printing of lots with small number of pages, there is observed a tendency that the market is shifting to on-demand printing using an inkjet process. Generic offset printing paper is made for a specification of an oil-based ink, and its absorbency of a water-based ink is extremely poor. Thus, the ink does not uniformly wet and spread and bleeds severely, and there are big problems of especially degradation of beading quality and image drying properties and fixability right after printing in fast one-pass printing.
Accordingly, in inkjet recording on a recording medium, further in recording on offset printing paper using a water-based ink, a post-treatment liquid for inkjet recording which enables an image having superior beading quality and scratch resistance even in fast one-pass printing has been currently sought.